Alloys

ABSTRACT

A method of making a heat-recoverable article from a heatrecoverable alloy, which after suitable treatment changes its shape when appropriate temperature changes are made including the step of applying to the alloy in its high-temperature phase a strain which produces a stress which induces a desired shape for its low-temperature phase. The method may be used with new heatrecoverable alloys which are uranium binary alloys with molybdenum, niobium or rhenium, or manganese-copper binary alloys.

United States Patent v 11 1 Brook et al.

1451 Apr. 9, 1974 ALLOYS 3.450.372 6/1969 De Lange et al. 75/170 I2.914.433 11/1959 McGeary et al.... 75/122.7 x [751 Grevme Beaconsfield2.926.113 2/1960 McGearyetal. 75/122.7 x 5 lles lckenham, both of2.259.459 /1941 Dean 75/134 n OTHER PUBLICATIONS [73] Assigneez Fulm erResearch Institute Limited, Metal with a Memory for Shape... Iron AgeVOL Buckinghamshlre, England 203 (22) pg 98 (1969). [22] Filed: Apr. 30,1970 0 Primary E.\'z1miner-.-Carl D. uarforth [211 App! 33299 AssistantExaminerR. E. Schafer Attorney. Agent. or FirmBrady, OBoyle and GatesForeign Application Priority Data I May 1. 1969 Great Britain 22372/69[57] ABSTRACT A method of making a heat-recoverable article from a [52]U.S. C1. 148/115, -/122.7, 75/134 M,- heat-recoverable alloy. whichafter suitable treatment 75/ 1 70. 148/132 changes its shape whenappropriate temperature [51 1 Int. Cl C22f 1/00, C22f 1/06, C22f l/16Changes are made including the step of applying to the [58] Field ofSearch 75/122.7, 134 M, 170; alloy in its high-temperature phase astrain which pro- 148/115, 132 duces a stress which induces a desiredshape for its low-temperature phase. The method may be used with [56]References Cit d new heat-recoverable alloys which are uranium binaryUNITED STATES PATENTS alloys with molybdenum, niobium or rhenium, orman- 3.174.851 3/1965 Buchler 75/170 ganese'copper bmary alloys3.567.523 3/1971 Jackson et a1. 75/122.7 X 9 Claims, 5 Drawing Figures(7) Mn- 77 Vf/alfu Low temp. lieform at Heat under iiemnve restraint lawtemp. restraint at high temp. iii; :9 j:

(2) Mn 20 "/0 Eu Range without restraint :3 a...

flange after restraint :D D

(3) Ni- T/'(55/6Ni/ /Z5, (45" 30 Shape at ii. T. Hend ta angieiauledM3915? Heated Jr.

25 at ii. I. shape changes (4 spantaneausly ll 5 M0 q c C C Shape atIii. Bend ta Uathi]. Coal ta 7.9b[ ileat to iii.

spantaneaus shape change {/917 4115" a c Heat to 700% 0171 to iii. Lanlt0-795L' heat to ii].

--A/vns01nv.

float to [not to R]. [unite-7.95%

n (5) 10MB PATENTEDAPR 9 on 38021930 (7) Mn- 77 /g%Lu Low temp. eform atHeat under Hemove restraint low temp. restraint at high temp. a Ti 56 /oN/ i Mn- [u 2 Hange without restraint D Range after restraint Q Ni-T/(55/oN/ 30 Shape at 0.7. Bend to angle Cooled to 490C Heated to H. 7.

25 at H. T. shape changes (4 spontaneously 0 5 /o Mo C C Shape at 0].Bend to Hat/H. 00! to 406C Heat to H].

spontaneous shape change Heat to 700[ fool to 0.7. Lool to-7960 Heat to0.7.

90 A/vosoo/v.

Heat to 700%" fool to H]. Cool to-7.96l.

77 I (5 1 MB l/VVE N Tags ALLOYS This invention is concerned withimprovements in or relating to alloys.

It is known that certain alloys are heatrecoverable, that is to say,when a suitably heat-treated article of one shape made from the alloy iscaused to deform into another shape at an appropriate temperature andthe temperature is subsequently raised sufficiently, the article will atleast partly recover its original shape. This change of shape onreheating corresponds to a change of phase in the alloy from alow-temperature phase to a high-temperature phase. The effect ofheat-recovery is known to occur with nickel-titanium binary alloyscontaining 52-56 percent by weight of nickel and with certaingold-cadmium, cadmium silver-gold and indium-thallium alloys.

A characteristic of all heat-recoverable alloys appears to be that, oncooling, they undergo a shear transformation to a banded martensite orretain the high temperature form as quenched, but transform by shear oncold working. The key feature is apparently that, on shaping at a lowtemperature, a shear transformation occurs which may be of the formdescribed above or may be a change in the type of martensite. It seemsthat the strain accommodated by this shear transformation is recoverableon heating and it is on this recoverable strain that theheat-recoverable properties depend.

It will be understood that the expressions high-- temperature andlow-temperature are comparative and that, depending on the alloy, thehigh-temperature phase may exist for example at room temperature whilethe low-temperature phase exists at lower temperatures.

What we have discovered is that the strain to be accommodated at thelower temperature by the shear transformation can be applied at least inpart to the high-temperature phase at a temperature above thetemperature (the Ms transformation temperature defined hereinafter) atwhich transformation begins spontaneously and that it is a practicaladvantage to apply the strain in this way. The essential feature of ourinvention is therefore that a stress either external or internal, mustbe present before and during the shear transformation so as to activate,in our belief, martensitic nuclei of the appropriate orientation to givethe required shape change.

Difficulties have been experienced hitherto in taking practicaladvantage of the effect of heat-recovery and it is thus an object of thepresent invention to render all heat recoverable alloys more readilyuseful.

The invention provides a method of making a heatrecoverable article froma heat-recoverable alloy, which method includes the step of applying tothe alloy in its high-temperature phase a strain which produces a stresswhich induces a desired shape for its lowtemperature phase.

In one manner of performing the invention, saidstrain is applied bydeforming the alloy in its high-.

temperature phase partly towards the shape required for thelow-temperature phase and the temperature is subsequently lowered sothat the alloy changes into its low-temperature phase. The change intothe lowtemperature phase is accompanied by a continued change of shapeinto the desired shape without the 'application of an external force.This form of the invention is of great practical value since it providesa means of putting an alloy at a comparatively high temperature into acondition in which it will deform spontaneously at lower temperatures toa new shape which is dictated by the initial high temperaturedeformation. It is there- 'fore unnecessary to effect working of thealloy at'low temperatures. In practice, the metastable high temperaturephase of the alloy is cooled to between its Md and Ms transformationtemperatures. Md is the temperature of the start of the martensitictransformation under stress and Ms is the temperature of the start ofthe transformation without'applied stress. With'some alloys thetemperature should be as close to the Ms transformation temperature aspossible, e.g. within 10C, to obtain the desired residual internalstress by said partial deformation. In .other alloys a greater margin oftemperature above Ms is possible. A suitable temperature for a givenalloy can readily be found by experiment. The alloy is then deformed asmall amountv (i.e. less than the final strain it is desired to putintothe low temperature phase). Cooling is continued to below the Mstransformation temperature when the alloy will continue to change inshape in the direction indicated by the prior deformation. On reheatingthis' change of shape is wholly or partly reversed-and on cooling againthe change in shape towards the low temperature'shape 'occursspontaneously. Continued heatingand cooling is accompanied by continuedchanges in shape.

' In another manner ofperforming the invention, the alloy is deformedinto a desired shape in its lowtemperature phase and said strain isapplied by raising the temperature so that the alloy changes into itshightemperature phase while restraint is applied to the alloy to preventa change in shape. Thus, according to one aspect of the invention, thereis provided amethod of making a heat-recoverable article from aheatrecoverable alloy, which method includes the steps of shaping thealloy at an elevated temperature into a first shape,'cooling to a lowertemperature, deforming the alloy at the lower temperature into a secondshape, said temperatures being such that if reheated without restraintto an appropriate temperature the alloy would at least partly resume itsfirst, shape, and reheating the alloy to said appropriatetemperaturewhile subjecting it to restraint which prevents a-changeof shape.Depending on the temperaturesinvolved and the intended use of thearticle, the alloy may be cooled to the lower temperature afterreheating, still retaining the second shape. Then'if the alloy isreheated without restraint it will change wholly or partly to its firstshape but on cooling will revert wholly or partly to its second shape.-

Continued heating and cooling is accompanied by con thought to beobtained by partial initial deformation before cooling tothe'low-temperature phase,when it is considered that sufficient nucleiof the low temperature martensitic phase are activated by the initialdeformation on such orientations that on cooling the alloy continues itschange of shape.

Reheating under restraint is particularly useful since it enables theupper temperature to which the alloy is heated to be so far above thetransformation temperature that continued reversibility of shape wouldbe lost in the absence of restraint. Nevertheless, the upper temperaturemust not be sufficient for relaxation of stress to occur by plasticdeformation, e.g. creep, or reversibility will be lost.

In all cases, the temperature to which the alloy is heated should be toolow for ageing or tempering of the alloy to take place. If precipitationoccurs, the alloy assumes its high temperature shape permanently.

Reheating under restraint may also be used to change the positionsbetween which change of shape occurs (but not the amount of change) inalloys which have a low yield stress and deform plastically, such as abinary alloy of manganese containing 20 percent copper and a binaryalloy of uranium containing percent molybdenum as hereinafter described.

We have found that the restraint need not always be applied by externalmechanical means such as a jig. In some cases, an oxide skin, a metalcoating or the like can provide the necessary restraint. We have notedthat alloys which, in the as-quenched or rapidly cooled condition, havea strong heat-recovery effect, also have a high internal friction ordamping capacity and exhibit an anomolously low pseudo-elastic moduluson loading but a normal modulus typical of the slowly cooled alloy onunloading.

We have found further alloys which possess the above properties and areheat-recoverable. These alloys are uranium-molybdenum binary alloyscontaining 2 to 7% (preferably 3 to 6.5%, e.g. about 4%) by weightmolybdenum, uranium-niobium binary alloys containing 3 to 11%(preferably 4 to e.g. about 6%) by weight niobium, uranium-rheniumbinary alloys containing 2 to 7% (preferably about 4%) by weight rheniumand manganese-copper binary alloys containing 5 to 50% (preferably, formost uses 5 to by weight copper.

By a binary alloy is meant an alloy consisting essentially of the twometals specified with or without impurities and/or incidentalconstituents which do not effect the crystal structure or metallurgicalproperties so as to prevent the heat-recovery effect from existing.

All the above-mentioned uranium and manganese binary alloys can bereadily fabricated from cast ingots without difficulty, e.g. by rolling,forging or extrusion as desired,

EXAMPLES URANIUM BINARY ALLOYS Uranium binary alloys were treated in theform of strip, 1 mm thick, where the application required that thematerial bend or flex on recovery, and in the form of rod or tube wherethe application required that the material change shape longitudinally(rod) or laterally (tube). The material was heated in a protectiveatmosphere or in a vacuum at a temperature within the y phase field(e.g. 800 C) for a short time depending on its thickness. It was thencooled rapidly e.g. in water or oil or a jet of cold gas or by radiationif the section was small, so as to prevent precipitation of the a phaseor eutectoid. The material was cooled to a temperature below the Mstransformation temperature, at which the transformation to bandedmartensite occurs. At this temperature, the material was deformed fromits original shape e.g. by bending strip, or stretching or compressingthe rod or expanding the tube or by deforming it as desired. Onreheating above a critical temperature, the original shape was at leastpartly restored.

In uranium-molybdenum binary alloys, at least 2%Mo by weight was needed.However, in an alloy with as little as 2%Mo, the amount of strain whichcould be applied at ambient temperature was very small and thetemperature to which the alloy must be reheated to reverse the shapechange was approximately 500 C at which rapid precipitation of a phaseoccurs. An alloy containing 3%Mo could be deformed at ambienttemperature and started to recover its original shape at 350 C andcompleted the recovery at 450 500 C. However, exposure to 500 C for morethan l0-30 minutes cumulatively caused a phase and eutectoid to formafter which the heat-recoverable property was lost.

Alloys with more than 3% and less than 5%Mo are most useful in practice.An alloy containing 4%Mo could be deformed at ambient temperature andstarted to recover its shape on heating to 200 C. For example, astraight 1mm thick strip of this alloy was bent through an angle of 100at ambient temperature. On heating for 3 minutes at 250 C, the strippartially straightened to 30 and on cooling to ambient temperature, themovement was reversed to In this example, it was noticed that restraintwas applied by a thick oxide skin formed by heating at 800 C ininadequate vacuum.

An alloy containing 4.5%Mo was also examined. A strip was bent atambient temperature and started to straighten at C. On heating to 250 C,almost complete recovery of the original shape was obtained and littlereversal took place on cooling to RT. For example, a straight strip bentthrough,l20 at ambient temperature recovered to 30 after 3 minutes at100 C. On cooling ambient temperature, reversal to 45 occurred. If therecovery temperature was raised to 250 C, more complete recovery wasobtained and the amount of reversal was less e.g. a straight strip bentthrough 90 at ambient temperature recovered to 5 at 250 C and reversedto 10 on cooling to ambient temperature.

It will be seen that the amount of reversal on cooling decreases as thereheating temperature is raised.

An alloy with 5%Mo started to recover'on heating to 50 C and almostcomplete recovery occurred at 250 C e.g. a straight strip was bent to aspecific angle at room temperature (R.T.) and then heated to atemperature T and then cooled to room temperature and the followingtable shows the amount of recovery.

Temp. to which Angle of Angle after Angle after strip heated. Tdeformation at recovery at T cooling to R.T.

60C 80 20 30 100C 10 20 150C 15 30 200C 10 15 250C 90 5 10 U-shape l96Cl96C R.T. 100C by deforming l96C W4 l96C and so on An alloy with 6%Modid not transform to the martensitic structure until cooled below roomtemperature. When a strip deformed to a U-shape at ambient temperaturewas heated to 100 C, only a slight change in shape occurred. TheU-shaped piece was cooled to a temperature approximately 80 C and wasdeformed by straightening completely. On reheating to ambienttemperature, the strip recovered to a U shape again. As the molybdenumcontent was increased to 7%, the temperature at which deformation mustbe carried out was lowered. 7% Mo represented the practical upper limitwhen deforming at temperatures down to l96 C.

Uranium-niobium binary alloys behaved in a similar way to U-Mo alloys.3% Nb was needed to obtain the same effect as 2%Mo but such an alloy wasof little practical use as the amount of recoverable deformation wassmall and the temperature of recovery so high that a and eutectoidformation occurred and no further recovery was possible. With 4%Nb,recovery was possible at 350 C and with 5% Nb, recovery occurred at 250300 C, after deformation at ambient temperature. 7%Nb alloy recovered atabout 100 C and is comparable to a 5%Mo alloy. Alloys with 8 to 10%Nbcould be deformed at --80 to l96 C and recover on heating to ambienttemperature.

U-Re binary alloys containing 2'to 7% rhenium behave in like manner.

Experiments were also carried out with a inch diam rod ofuranium-molybdenum binary alloy containing 5%Mo. The specimen was cooledto l96 C at which temperature it was compressed 3.8%. On reheating toambient temperature, the specimen expanded 3.2% over and above thenormal thermal expansion. Another rod specimen was cooled to l96 C andwas then compressed 4%. It was then reheated to room temperature butunder restraint so that the expansion on recovery was prevented. Astress of 73,900 lbf/in was developed. This demonstrates another use ofthis invention in developing a force capable of doing work.

MANGANESE COPPER BINARY ALLOYS These alloys were treated and testedsimilarly to the uranium alloys.

An alloy containing 5% to approximately copper showed heat-recoveryeffects if the low temperature at which deformation took place was about150 C for 5%Cu to about 100 C for 10%Cu and 50 C for 15%Cu. These alloysthen recovered their shape partially on heating to 250 C. The shapechange was con.- tinuous over this temperature range.

17.5% copper alloy recovered after deformation at room temperature whenit was heated to l50 C. The amount of recovery was not 100% but thechange was reversible e. g. when a 1mm thick strip of this alloy wasdeformed into a U-shape with the tips of the legs of the U separated by2.7mm at 25 C heating to 150 C expanded the separation of the tips to4.5mm. On cooling to 25 C, the tips closed to 3.7mm. Reheating to 150 Cexpanded the tips again to 4.5mm and cooling to 25 C reversed this to365mm.

17.5% Cu alloy demonstrated recovery more effec- Q tively when it wasdeformed at -1 96 C. A U loop with a separation between the tips of thelegs of 3.95mm expanded to a separation of 5.5mm on heating to 25 C,6.8mm at 100 C and virtually straightened at C. On cooling theseparation reduced to'6.4mm at 100 C, 6.2mm at 25 C and 5.95mm at l96 C;It expanded to 625mm again at 25 C.

25%Cu alloy was deformed at room temperature and heated to highertemperatures but no recovery occurred. This was as expected because atroom temperature the 25%Cu alloy deforms by plastic deformation and notby shear transformation. It was necessary to cool this alloy and deformat l96 C. On deforming at l96 C and heating this alloy, it behaved likethe 17.5%Cu alloy except that most deformation was recovered between 196C and room temperature and less between room temperature and l00 C.Cooling down again caused reversal of the change of shape, and changesof shape continued with repeated heatingand cooling. I

Like all of the other manganese-copper alloys, the- 25% Cu alloy changedin shape over a considerable range of temperature and not sharply over anarrow range. v

With 30 to 50% Cu alloys it is necessary to cool and deform the alloywell below l96 C. This makes the alloys useful for special cryogenicapplications.

The lack of complete recovery in the Mn-Cu alloys can be explained bythe fact that their yield stress is relatively low and the reversal ofthe transformation is taken up by plastic strain in the hightemperaturephase as it forms. This was demonstrated by deforming a stripof Mn-Cu binary alloy containing 17.5%Cu at low temperature into U-shapeand heating under restraint. When the restraint was removed at hightemperature, no change in shape occurred. When a strip of material ofhigh yield stress (in the test a nickel-titanium binary alloy containing56% nickel was used) was treated in the same way, the U-shaped stripsprang open when the restraint was removed at high temperature. Theaccompanying drawing shows these changes at (1'). 1

APPLICATION OFSTRAIN TO INDUCE INTERNAL STRESS An example of an effectof reheating under restraint I has been given above in connection with amanganesecopper binary alloy containing 17.5%Cu and a nickel- -titaniumbinary alloy containing 56%Ni'.

(between the Ms and Md temperatures but nearer to the Ms temperature),deforming the specimen a small amount (i.e. less than the finaldeformation needed inthe low temperature form), continuing cooling tobelow the Ms transformation temperature, during which the specimencontinued to change in shape in the direction indicated by the priordeformation. On

reheating this change in shape is wholly or partly reversed and oncooling again the change in shape occurs spontaneously.

A test on a strip of nickel-titanium binary alloy containing 56%Niheated to 850 C and quenched to room temperature in the flat conditionis illustrated in the accompanying drawing at (3).

The strip was bent through an angle of 25 at room temperature. Oncooling to l96 C the angle changed spontaneously to an angle of 45. Onheating again to room temperature the angle changed to 30. On heatingand cooling between room temperature and l96 C, the angle of the stripchanged from 30 to 45 reversibly.

A test on a strip of uranium-molybdenum binary alloy containing Mo,heated to 800 C and quenched to room temperature in the flat conditionis illustrated at (4) in the accompanying drawing.

The strip was bent to U-shape at room temperature. It was cooled to 1 96C when its shape changed spontaneously, the legs of the U moving towardseach other and crossing. Heating to room temperature nearly restored theU-shape so that a C-shape was formed. Continued heating to 100 C causedthe strip to become flat again. Subsequent cooling to room temperaturecaused the strip to assume a right angle shape and further cooling to 196 C caused it to became C-shaped again. Reheating to room temperatureresulted in an angle of 85 between the legs of the strip and furtherheating to 100 C caused the strip to flatten. Cooling to roomtemperature resulted in a right angle shape and further cooling to 1 96C resulted in a C-shape. On continued heating and cooling, the shapechanges continued in the same way. It will be seen that hysteresisoccurs so that at room temperature the shape is slightly different whenheating and cooling. The original shape at l96 C is not recoveredcompletely, but it is considered that cooling below l96 C would causecomplete recovery of the original shape because there is hysteresis atl96 C as well as at room temperature.

A test on a strip of manganese-copper binary alloy containing 17.5%Cushowed that when partly deformed into a U-shape at room temperature andthen cooled to l96 C, the legs of the U moved towards each other toclose the U. A 20%Cu alloy gave the same results but even more movementwas obtained.

Articles made by the methods and from the heatrecoverable alloysdescribed herein are useful for many purposes where a change of shape isnecessary. For example, they may be used as tubes in couplings, whichtubes change shape to grip two elements to be connected together, astemperature-responsive elements in switching devices, and as formers ordies on which a plastics or metal sheet is shaped whereafter the formeror die is caused to shrink away, allowing the removal of the shapedsheet and the former or die is then caused to revert to its originalshape for the next operation. The accompanying drawing at (5) shows atemperature-responsive switch having three contacts 10, 11 and 12. Abent strip 13 made by a method and of an alloy as hereinbefore describedmakes an electrical connection between the contacts and 11 at onetemperature and between the contacts 10 and 12 at a differenttemperature.

We claim:

1. A method of making a heat-recoverable article from a heat-recoverablealloy, which article is repeatedly changeable in shape from a firstshape towards a second shape by lowering its temperature and from thesecond shape towards the first shape by raising its temperature, saidchanges in shape corresponding to changes in phase in the alloy from ahigh-temperature phase to a low-temperature phase and from thelowtemperature phase to the high-temperature phase respectively, whichmethod comprises the steps of deforming the alloy in its low-temperaturephase so as to change its shape from the first shape to the secondshape, applying restraint to the alloy in the second shape so formed,raising the temperature so that the alloy changes into itshigh-temperature phase while said restraint prevents a change in shape,and subsequently repeatedly altering the temperature to cause saidchanges in shape without applying any further deformation to the alloy.

2. A method according to claim 1 in which after raising the temperaturewhile applying said restraint the alloy is cooled so that it changesinto its lowtemperature phase, still retaining said second shape.

3. A method according to claim 1 in which the alloy is selected from thegroup consisting of binary alloys of uranium containing 2 to 7% byweight molybdenum, 3 to l 1% by weight niobium and2 to 7% by weightrhenium.

4. A method according to claim 1 in which the alloy is amanganese-copper binary alloy containing 5 to 50% by weight'copper.

5. A method according to claim 1 in which the alloy is a nickel-titaniumbinary alloy containing 52 to 56% by weight nickel.

6. A method of making a heat-recoverable article from a heat-recoverablebinary alloy selected from the group consisting of uranium-molybdenumcontaining 2 to 7% by weight molybdenum, uranium-rhenium containing 2 to7% by weight rhenium, manganese-copper containing 5 to 50% by weightcopper and nickeltitanium containing 52 to 56% by weight nickel, whichmethod includes the steps of deforming the alloy in its high-temperaturephase partly towards the shape required for the low-temperature phase,thereby applying to the alloy in its high-temperature phase a strainwhich produces a stress which induces a desired shape for itslow-temperature phase, and subsequently lowering the temperature so thatthe alloy changes into its lowtemperature phase and assumes the requiredshape.

7. A method of making a heat-recoverable article from a heat-recoverablebinary alloy selected from the group consisting of uranium-molybdenumcontaining 2 to 7% by weight molybdenum, uranium-rhenium containing 2 to7% by weight rhenium and manganesecopper containing 5 to 50% by weightcopper, which method includes the steps of shaping the alloy at anelevated temperature into a first shape, cooling to a lower temperature,and causing the alloy to deform at the lower temperature into a secondshape, said temperature being such that if reheated to an appropriatetemperature the alloy would at least partly regain its first shape.

8. A method according to claim 7, in which the alloy is a binary alloyof uranium containing 3 to 6.5% by weight molybdenum.

9. A method according to claim 7 in which the alloy contains 5 to 30% byweight copper.

2. A method according to claim 1 in which after raising the temperaturewhile applying said restraint the alloy is cooled so that it changesinto its low-temperature phase, still retaining said second shape.
 3. Amethod according to claim 1 in which the alloy is selected from thegroup consisting of binary alloys of uranium containing 2 to 7% byweight molybdenum, 3 to 11% by weight niobium and 2 to 7% by weightrhenium.
 4. A method according to claim 1 in which the alloy is amanganese-copper binary alloy containing 5 to 50% by weight copper.
 5. Amethod according to claim 1 in which the alloy is a nickel-titaniumbinary alloy containing 52 to 56% by weight nickel.
 6. A method ofmaking a heat-recoverable article from a heat-recoverable binary alloyselected from the group consisting of uranium-molybdenum containing 2 to7% by weight molybdenum, uranium-rhenium containing 2 to 7% by weightrhenium, manganese-copper containing 5 to 50% by weight copper andnickel-titanium containing 52 to 56% by weight nickel, which methodincludes the steps of deforming the alloy in its high-temperature phasepartly towards the shape required for the low-temperature phase, therebyapplying to the alloy in its high-temperature phase a strain whichproduces a stress which induces a desired shape for its low-temperaturephase, and subsequently lowering the temperature so that the alloychanges into its low-temperature phase and assumes the required shape.7. A method of making a heat-recoverable article from a heat-recoverablebinary alloy selected from the group consisting of uranium-molybdenumcontaining 2 to 7% by weight molybdenum, uranium-rhenium containing 2 to7% by weight rhenium and manganese-copper containing 5 to 50% by weightcopper, which method includes the steps of shaping the alloy at anelevated temperature into a first shape, cooling to a lower temperature,and causing the alloy to deform at the lower temperature into a secondshape, said temperature being such that if reheated to an appropriatetemperature the alloy would at least partly regain its first shape.
 8. Amethod according to claim 7, in which the alloy is a binary alloy ofuranium containing 3 to 6.5% by weight molybdenum.
 9. A method accordingto claim 7 in which the alloy contains 5 to 30% by weight copper.